1. Field of the Invention
The present invention is related to an image display device. Especially, the present invention is related to an image display device in which position adjustment between a semiconductor circuit and a color filter is easy and reliability is high.
2. Description of the Related Art
A thin film transistor having an amorphous silicon or a polycrystal silicon has been generally used for a transistor for driving an electronic device. However, since the amorphous silicon and the polycrystal silicon are not transparent and are optically sensitive in the region of visible light, a light shielding film is necessary. Therefore, since a semiconductor circuit including a thin film transistor, a wiring thereof and the like becomes a problem in visibility, the semiconductor circuit has been arranged in a back side of an observation side of an image display element.
A color filter is generally used in order to make a full-color reflective type display device such as a reflective type liquid crystal display device and an electrophoresis display device. However, from the above-mentioned reason, a liquid crystal sealing layer or an electrophoresis particle layer is formed between a color filter and a thin film transistor substrate. However, if a color filter and a semiconductor circuit substrate are formed at such positions, for example, in the case of a liquid crystal, after a liquid crystal is sealed, position adjustment between a semiconductor circuit and a color filter is needed. Therefore, it is difficult to achieve a high accuracy. This cause an increase of costs and a reduction of yield. Therefore, research and development are performed in order to realize a display device in which a transparent semiconductor circuit is directly formed on a color filter, thereby the position adjustment is easy.
If a display has such a structure, position adjustment between a color filter and a semiconductor circuit becomes easy. However, in the case of this structure, because a semiconductor circuit is arranged in a front side of an image display element, the front side being a viewer side, false operation of a thin film transistor may occur when a semiconductor circuit is irradiated with outside light such as sunlight. In fact, it was found that an oxide semiconductor is transparent while band gap thereof is frequently 3.0 eV-3.5 eV, thereby false operation of a thin film transistor occurs by photoelectric current flowing in a semiconductor active layer by irradiation with sunlight in the case where the band gap is within such a range. Therefore, it was found that a problem in displaying an image occurs in the case where a display having such a structure is used at a very bright place such as a outdoor place. In addition, this type image display device is disclosed, for example, in the following non-patent document.
One of the many objects of the present invention is to provide an image display device in which position adjustment between a semiconductor circuit and a color filter is easy and reliability is high.
[non-patent document] M. Ito et al., Proc. 13th IDW, 585 (2006)